1. Field
The disclosed and claimed concept relates generally to nuclear power plants, and, more particularly, to a measurement apparatus that is operable to determine the amount of compressive loading that will be applied between a spring and a dimple of a grid of a pressurized water reactor to a fuel rod situated between the spring and the dimple.
2. Related Art
Nuclear power plants may be of various configurations. One type of nuclear power plant employs a nuclear reactor to generate steam which is employed to turn one or more turbines that operate electrical generators. One type of reactor is a pressurized water reactor (PWR). Such a PWR operates by heating water within a primary cooling loop which is maintained at an elevated pressure. A steam generator, which can be characterized as a type of heat exchanger, thermally connects the primary cooling loop with a secondary cooling loop and generates steam in the secondary cooling loop. The secondary cooling loop is connected with the turbines and with a heat sink such as a cooling tower.
In most pressurized water nuclear reactors, a reactor core is comprised of a large number of elongated fuel assemblies. These fuel assemblies typically include a plurality of cylindrical fuel rods that are held in an organized array by a plurality of grids that are spaced axially along the length of the fuel assembly and are attached to a plurality of elongated thimble tubes of the fuel assembly. The thimble tubes typically receive control rods or instrumentation therein. Top and bottom nozzles on opposite ends of the fuel assembly are secured to the ends of the thimble tubes that extend slightly above and below the ends of the fuel rods.
The grids are formed of straps of metal that are connected together to form a plurality of cells. Each cell generally has a spring/dimple pair that engages a fuel rod therebetween and has another spring/dimple pair that similarly engages the fuel rod. As a general matter, the spring of each spring/dimple pair is relatively more compliant than the corresponding dimple of the spring/dimple pair. One spring/dimple pair retains the fuel rod in one direction transverse to the longitudinal extent of the fuel rod, and the other spring/dimple pair retains the rod in another direction transverse to the longitudinal extent of the rod. While such grids and their spring/dimple pairs have been generally effective for their intended purposes, they have not been without limitation.
As is generally understood in the relevant art, the springs and dimples of the grids can become relaxed over time due to factors such as heat, neutron bombardment, fatigue, and other such factors. As such, it is desirable to periodically assess the amount of compressive load that will be applied by the springs and dimples to the fuel rod to assess whether remedial action is needed. Previous systems for measuring the compressive load have, however, met with limitations since they were capable of determining only whether the overall load of two spring/dimple pairs within the cell had insufficient compressive loading and were therefore unable to assess whether an individual spring/dimple pair was deficient in its compressive loading. Improvements thus would be desirable.